I have been oxygenating my wort with a sintered SS airstone attached to teh small bernzOmatic oxygen bottles they sell for light duty mixed-gas welding. I am very happy with the results - 2 30 second bursts and the wort is well saturated. I have actually had to start adding a half-pound of dextrine malt to all my grists so that I don't under-attenuate if I'm using an attenuatiev yeast strain. One 'yea' vote for oxygen.

I used to use oxy, but then I discovered the all powerful(and cheap) fish air pump. For a little time investment and a filter, the fish pump works as well if not better due to the fact you cannot over saturate with air, however you can with pure oxygen, not to mention the potential flammage which should not be present when drinking errrr brewing with propane nearby.

What I would be using, is a mixture of Oxygen, and filtered air. Standard air oxygen content is 20.5% oxygen. I'm thinking of using 40% oxygen, more effect of oxygen, but I will not be risking contamination like you do with an air pump. What kind of filter is used with an air pump that you get at the fish store?

When I operated my brewing microbiology company, we used ambient air to supply aeration to our propagation vessels. We used sintered stainless steel stones with a high velocity air pump to supply air through a sterile filter. The vessels were fitted with magnetic drives that rotated paddles in the vessel. Air was injected and stirred 24 hours a day until the desired cell concentration was reached.

You can do the same thing at home, but there are a couple of rules:

1)It is REQUIRED that you use a .3 ~ .1 micron, autoclavable filter between the pump and the stone that is designed for air, not liquid. (Note: if you use medical grade O2, you don't have to use the filter. If you use aviator grade or industrial grade which is usually welding/brazing O2... ie those Bernzomatic cylinders and others, it is highly recommended to use a filter. Using these filters, when properly sterilized, will yield microbiologically sterile air.

2) DON'T use a stone designed for aquariums. These can quickly break down in the presence of low pH or high pH solutions... READ SANITIZERS !. Also, wort is acidic as well. They cannot be heat sanitized either.

Purchase a .5 micron stainless steel sintered stone, preferably with a stainless steel stem attached. This way you only have to autclave the stemmed stone and a short length of tube that goes from the filter to the stem supplying the stone. The tubing leading to the filter from the pump does not have to be sterilized as the filter will take care of any "meanies".

3) The rule in propagation is STERILIZATION, not sanitization. Wort spoiling bacteria grow at over 10 times the rate of brewing yeast ! No matter whether using air or O2, everything used has to be autoclavable via steam to ensure sterility. This is easily done using a pressure cooker for 20 minutes. Use pyrex lab glassware, a stainless steel sintered aeration stone, a single hole white rubber bung and vinyl tubing. All of these items can be steam sterilized. The tubing life will be reduced, but it is cheaply replaced. If you really want to make your starters cook... use a magnetic stirrer. The coated magnetic bars are also autoclavable.

4) Most aquarium pumps can't produce enough head pressure to overcome the resistance created by a .3 or .1 micron filter in combination with a .5 micron stone.

When I propped at home, I bought a pump from St. Pats that could drive 2 stones simultaneously and was only about $20. They no longer offer this one, but I looked at their site and they have one for under $10 that they say will work with their stones, which they claim require less pressure. I haven't tried this combination, but my experience has shown that they don't tend to mis-represent their products, so the combination probably works fine.

5) The point of propagation is cell density increse, not fermentation. The yeast reproduction phase requires oxygen whereas fermentation is anaerobic. So, there are 2 things to keep in mind:

1) Once the oxgen level drops, they metabolically shift into fermentation. So if using ambient air, you should continuously aerate the media up to within 2~3 hours of pitching. Stopping the aeration 2~3 hours short of pitching time allows the yeast to begin their shift to anaerobic fermentation phase. It is virtually impossible to over oxygenate using ambient air.

2) Since the point of propagation is yeast cell increase, reproduction is what you are attempting to maximize. Most starter directions on smack packs or RTP tubes state that you should make a prop. media that approximates the gravity of the wort in which you intend to pitch. This is true if you don't aerate. If aerating, you will be holding the yeast in the reproduction phase, so they don't need much sugar to metabolize as they consume glycogen instead that has been stored in their cell membranes. So, preparing a starter at a gravity above 1.025 is only a waste of malt. They will only begin eating majority of the sugars once the media becomes anaerobic. This is why you should rest the propagate 2~3 hours prior to pitching.

Now... where to get this stuff:

Lab glassware and the filters are available through lab suppliers such as Cynmar, Fisher Scientific and Daigger (www.daigger.com). The hombrew suppliers that are more advanced also offer some or all of these items and have the stainless steel aeration stones and stems... St. Pats ( http://www.stpats.com/diffuser.htm) , Beer, Beer & More Beer ( http://www.morebeer.com/catalog.php3?secID=yeast ) , Williams Brewing ( http://www.williamsbrewing.com/ then enter "aeration" in the search box) ... etc... The filters sold by St. Pats run $ 8.75 each, but a better constructed filter with a larger surface area (read better flow, easier on your pump, will last longer) is made by Gelman, which is what I used in my lab. These are available from Daigger ( http://www.daigger.com/catalog/product? ... odId=8446L) and are $ 13.71 each in 3 packs. These appear to also be the same filters sold by Beer, Beer & More Beer and are sold individually for more money, of course!

How did Mesa type all that in the time it took for me to respond? Wow. I know, he already knows what we are going to ask and prewrites it. Or maybe he has one of those voice transfer programs! We bow oh master brewer.

My two cents: I run that pump before pitching abount 1hr. and leave it on after pitching for 10 min. if it doesn't foam over.

Like the GREAT MESA said, you can't over do it with air. I use a good air pump with a .3 micron filter and SS stone as descibed below.

Sterilization is required when propagating a culture or volumizing a starter. It would be nice if we could sterilize the primary, but I don't know of a way to do that unless you are using stainless steel fermenters. Then you could sterilize with boiling water.